Nina Totenberg

Immigration and border-patrol issues took center stage at the U.S. Supreme Court in two cases on Tuesday.

A sharply divided court first ruled that the parents of a Mexican boy shot and killed by a U.S. border patrol agent cannot sue the officer who killed their son. Then, the court heard arguments in a free-speech case that will determine whether people who encourage illegal immigrants to remain in the country can be prosecuted.

Border Patrol shooting

Updated at 8:34 p.m. ET

Like it or not, Chief Justice John Roberts finds himself drawn into impeachment controversies perhaps more than he anticipated. Over a 24-hour period, he has twice refused to put a question from Sen. Rand Paul, R-Ky., to the House impeachment managers and lawyers for President Trump.

In a case with potentially profound implications, the U.S. Supreme Court's conservative majority seemed ready to invalidate a provision of the Montana state constitution that bars aid to religious schools. A decision like that would work a sea change in constitutional law, significantly removing the longstanding high wall of separation between church and state.

The U.S. Supreme Court hears arguments Wednesday in a major case that could dramatically alter the line separating church and state.

At issue is a Montana state constitutional amendment that bars direct and indirect taxpayer aid to religious institutions. Conservative religious groups and advocates of school choice are challenging the "no-aid" provision.

There were some acerbic and personal comments from the justices of the Supreme Court on Wednesday, as they heard an age discrimination case that could affect more than a million federal workers over the age of 40.

The federal law says that "all personnel decisions" made in the federal workforce "shall be made free from age discrimination."

The Equal Employment Opportunity Commission has long interpreted that to mean that if a federal worker can show that age was a factor in denying her a job or promotion, the worker is entitled to back pay or other remedies.

The U.S. Supreme Court on Tuesday weighed whether to make life more difficult for prosecutors in public corruption cases.

The modern-day court has made it increasingly difficult to prosecute public officials who abuse their power but don't personally enrich themselves. The court has thrown out multiple public corruption convictions in recent years, all but eviscerating broad statutes aimed at ensuring the honest services of public employees.

"Bridgegate" was the political scandal that marked the beginning of the end of New Jersey Gov. Chris Christie's presidential hopes. The scandal's legal consequences could prove more consequential if, as prosecutors fear, the criminal convictions in the case are thrown out by the Supreme Court.

On Tuesday, the justices will revisit the case that made headlines in 2013 on the first day of school when, unbeknownst to the public, officials close to Christie ordered the shutdown of two of three access lanes from Fort Lee onto the George Washington Bridge.

When the Senate impeachment trial of President Trump opens, the man in the center chair will be Chief Justice John Roberts. His role is spelled out in the Constitution.

Twenty-one years ago Thursday, as the House approved articles of impeachment against President Bill Clinton, Senate Majority Leader Trent Lott was sitting in his study in Pascagoula, Miss., "looking out on a beautiful live oak tree." With a sigh, the Republican leader picked up the phone to call Senate Minority Leader Tom Daschle, his Democratic counterpart.

"Whether we like it or not, this is sitting in our lap," he told Daschle, "and we've got to figure out how to deal with it."

Lott was a skilled vote-counter.

The U.S. Supreme Court examined Obamacare for the fifth time on Tuesday, only this time the justices cast their skeptical gaze on Republican efforts to hobble the law.

Enacted by a Democrat-controlled Congress in 2010, the Affordable Care Act promised to partially reimburse insurers if they lost money by covering people with preexisting conditions. The law said that the government "shall" make these payments. But in 2015, Republicans, by then in control of both houses of Congress, attached riders to appropriations bills barring the use of the money for the promised payments.

The arc of partisanship in impeachment, to some extent, matches the increased polarization of politics in America over the last 45 years. It moves from consensus to deadlock.

When the House Judiciary Committee votes on articles of impeachment against President Trump, the vote is expected to be along purely partisan lines — a far cry from the committee impeachment vote against President Richard Nixon in 1974, and different too from the President Bill Clinton's impeachment in 1998.

Guns: when and how to regulate them. It's one of the biggest issues across the country. But the U.S. Supreme Court has rarely weighed in on the issue. In modern times, it has ruled decisively just twice. Now it's on the brink of doing so again.

With the retirement of Justice Anthony Kennedy, there now are five conservative justices who may be willing to shut down many attempts at regulation, just as the NRA's lock on state legislatures may be waning.